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In this paper, a robust digital watermarking algorithm against shearing is introduced. The proposed method makes use of the complete generalized orthogonal properties of orthogonal function system to achieve the piece-based orthogonal transform on the image. To strengthen the robustness of watermark, the significant middle frequently coefficients in the transformation matrix are picked up, based on characteristics of the image visual system. The watermark is adoptively weighed to the middle frequently matrix. The method improves the validity of watermarking and shows excellent advantage against shearing attack. Experimental results show that The watermark thus generated is invisible and performs well in StirMark test and is robust to geometrical attacks.